KR20110118273A - Method for encrypting and decrypting stream and cryptographic file systems thereof - Google Patents

Abstract

Embodiments relate to a stream encryption method.
In the stream encryption method according to the embodiment, generating a root key to be used for file system encryption, generating a plurality of sub-keys from the root key through a hash function to form a key tree, a plurality of sub-keys configured in the key tree And mapping data blocks configured in storage of the cipher file system, and generating a ciphertext stream by performing an XOR operation on a plurality of subkeys mapped to the data blocks and a plaintext stream.

Description

Hash tree-based stream encryption and decryption method and cipher file system {METHOD FOR ENCRYPTING AND DECRYPTING STREAM AND CRYPTOGRAPHIC FILE SYSTEMS THEREOF}

A stream encryption / decryption method and a cryptographic file system.

With services such as “Amazon Simple Storage Service (S3)” enabled, the market for storage outsourcing services is growing, in which user information is stored on central servers rather than on their computer devices. These services allow the storage device to be leased and used as needed without expansion of the storage device, thereby increasing convenience.

However, the activation of these services introduces new security problems. In other words, the user's information is stored in another server on the Internet instead of his own PC, etc., a problem of confidentiality occurs. Confidentiality is becoming an important issue as the storage location of user information is changed, which has nothing to do with it without any encryption.

To solve this problem, a cryptographic file system has been developed. The encrypted file system refers to a system for encrypting and storing user data, rather than storing it as it is.

Data encryption refers to the conversion of valuable information (plain text, plain text) into a form in which a third party does not know its meaning (cipher text), which is converted into cipher text using an encryption key. Can be. In contrast, data decryption means converting a cipher text into plain text. The cipher text stored in the storage device or transmitted over the communication line can be restored to the original information using the decryption key. Since a person who does not have a decryption key cannot correctly restore the original information, the information is protected unless the decryption key is known to a third party.

In general, data encryption methods are classified into block encryption algorithms and stream encryption algorithms.

1 is a diagram illustrating a concept of a block encryption algorithm. 2 is a diagram illustrating a concept of a stream encryption algorithm.

The block encryption algorithm is an algorithm for encrypting data in block units, and is an algorithm for encrypting in units of 128 bits.

The stream encryption algorithm is an algorithm that generates a random number by using a user's key as a seed key value and encrypts it through plain text and an XOR operation.

Each of these two algorithms has the following advantages and disadvantages.

The block encryption algorithm has an advantage that block-based access is possible because encryption is performed on a block basis. However, there is a disadvantage in that a very complicated calculation process is required compared to the stream encryption algorithm.

The stream encryption algorithm has an advantage that the operation speed is very fast because the encryption is performed through random sequence and plain XOR operation. However, in order to decrypt a specific block of encrypted data, it is necessary to generate a random sequence that was used to encrypt the block, and to do so, it is necessary to generate a random sequence by using a seed key value until the state is obtained. As a result, random accessibility is very low.

Therefore, although the general block encryption algorithm provides accessibility on a block basis, the operation complexity is higher than that of the stream encryption algorithm, and the stream encryption algorithm has an advantage of being much faster than the block encryption algorithm. The disadvantage is that accessibility is not provided.

An embodiment is to provide an encryption and decryption method capable of providing a fast operation speed of a stream encryption algorithm and accessibility on a block basis of a block encryption algorithm.

Embodiments provide an encryption file system capable of providing a fast operation speed of a stream encryption algorithm and accessibility in units of blocks of a block encryption algorithm.

The stream encryption method according to claim 1 is a stream encryption method in an encrypted file system, comprising: generating a root key to be used for file system encryption, and generating a plurality of subkeys from a root key through a hash function to construct a key tree Mapping a plurality of sub keys configured in the key tree and data blocks configured in storage of the cryptographic file system, and generating a cipher text stream by performing an XOR operation on the plurality of sub keys mapped to the data blocks and the plain text stream. It includes.

Comprising the key tree according to claim 2,

a. Dividing the value of the root key into a plurality of subsections, and generating a plurality of root keys having different subsection values by exchanging positions between the divided subsections, b. generating a plurality of root keys generated in step a as subkeys having different values using a hash function, c. dividing the value of the subkey generated through step b into a plurality of subsections, and generating a plurality of subkeys having different subsection values through position exchange between the divided subsections, and d. generating a plurality of subkeys generated through the step c as subkeys having different values using a hash function;

Compose a key tree by expanding a sub key through steps a through d, and compose a key tree with a depth h of a key tree satisfying the following formula,

m is the number of subsections, and n is the number of data blocks.

In accordance with another aspect of the present invention, there is provided a method for decrypting a ciphertext stream generated according to claim 1, comprising: deriving a plurality of subkeys mapped to a data block of storage through a hash function, and derived through a hash function Performing XOR operation on the plurality of sub-keys and the cipher text stream to generate a decrypted text stream.

The ciphertext stream stored in the storage is preferably accessible in units of data blocks.

The encrypted file system according to claim 5 is a system for stream encryption, comprising: a root key generation unit for generating a root key for file system encryption, and a plurality of subkeys from a root key through a hash function to construct a key tree A key tree configuration unit, a storage including a plurality of data blocks for storing a ciphertext stream, a mapping unit for mapping data blocks of a plurality of sub keys configured in the key tree, and a plurality of data blocks mapped to the data blocks of the storage And an encryption operation unit for generating a ciphertext stream by performing an XOR operation on the subkey and the plaintext stream.

Key tree structure according to claim 6,

An exchange operation unit and a key generation unit,

The exchange operation unit,

Divide the value of the root key into a plurality of subsections, generate a plurality of root keys with different subsection values through position exchange between the divided subsections, divide the value of the subkey into a plurality of subsections, and divide Generating a plurality of subkeys having different subsection values through position exchange between true subsections,

Key generation unit,

Generate a plurality of root keys generated through the exchange operator as sub keys having different values using the hash function, and generate a plurality of sub keys generated through the exchange operator using different hash functions. Generated by key,

The key tree component is

Compose the key tree by expanding the sub-keys through the exchange operation unit and the key generation unit, and compose the key tree by the depth (h) of the key tree satisfying the following formula,

m is the number of subsections, and n is the number of data blocks.

A cryptographic file system according to claim 7 is a system for decrypting a ciphertext stream generated according to the cryptographic file system of claim 5, comprising: a key derivation unit for deriving a plurality of subkeys mapped to a data block of a storage using a hash function; A plurality of sub-keys derived from the key derivation unit, and a decryption operation unit for generating an decrypted text stream by performing an XOR operation on the cipher text stream.

The ciphertext stream stored in the storage is preferably accessible in units of data blocks.

A cryptographic file system according to claim 9 is a system for stream encryption and decryption, comprising: a root key generation unit for generating a root key for file system encryption, and generating a plurality of subkeys from a root key through a hash function to generate a key tree; A key tree constructing unit, a storage including a plurality of data blocks for storing a ciphertext stream, a mapping unit for mapping data blocks of a plurality of sub keys configured in a key tree, and data blocks of the storage An encryption operation unit generating a ciphertext stream by performing XOR operation on a plurality of subkeys and a plain text stream, a key derivation unit deriving a plurality of subkeys mapped to a data block of a storage using a hash function, and a plurality of key derivation units derived from a key derivation unit. XOR operation on the subkey and the ciphertext stream to generate a decrypted text stream It includes.

Key tree structure according to claim 10,

An exchange operation unit and a key generation unit,

The exchange operation unit,

Divide the value of the root key into a plurality of subsections, generate a plurality of root keys with different subsection values through position exchange between the divided subsections, divide the value of the subkey into a plurality of subsections, and divide Generating a plurality of subkeys having different subsection values through position exchange between true subsections,

Key generation unit,

Generate a plurality of root keys generated through the exchange operator as sub keys having different values using the hash function, and generate a plurality of sub keys generated through the exchange operator using different hash functions. Generated by key,

The key tree component is

Compose the key tree by expanding the sub-keys through the exchange operation unit and the key generation unit, and compose the key tree by the depth (h) of the key tree satisfying the following formula,

m is the number of subsections, and n is the number of data blocks.

The ciphertext stream stored in the storage according to claim 11 is preferably accessible in units of blocks.

According to an embodiment, it is possible to provide an encryption / decryption method capable of providing a fast operation speed of a stream encryption algorithm and accessibility in units of blocks of a block encryption algorithm.

According to an embodiment, it is possible to provide a cryptographic file system capable of providing a fast operation speed of a stream encryption algorithm and accessibility in units of blocks of a block encryption algorithm.

1 illustrates a concept for a block encryption algorithm.
2 illustrates a concept for a stream encryption algorithm.
3 illustrates a concept of the present invention.
4 is a flowchart illustrating a stream encryption / decryption method according to an embodiment.
5 illustrates a method of constructing a key tree and a method of mapping a subkey and a data block, according to an exemplary embodiment.
6 is a diagram illustrating a process of generating a cipher text stream and storing it in a storage data block according to an embodiment.
7 is a diagram illustrating an overall process of storing and reading a file using a stream encryption algorithm according to an embodiment.
8 is a block diagram showing the overall configuration of a cryptographic file system according to an embodiment.
9 is a graph showing the performance comparison of the stream encryption algorithm (BA-RC4), the conventional block encryption algorithm (AES), and the stream encryption algorithm (RC4) according to the embodiment.

3 is a diagram illustrating the concept of the present invention.

Referring to FIG. 3, the present invention extends a key to be used for block-by-block encryption, and encrypts a block of data of a storage by a stream encryption algorithm using the extended key, thereby providing block-level access. to provide. Key expansion is accomplished through key tree construction using a one-way hash function. The stream encryption / decryption method and the cipher file system will be described later in more detail through embodiments.

Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. However, the accompanying drawings are only described in order to more easily disclose the contents of the embodiments, the scope of the present invention is not limited to the scope of the accompanying drawings will be readily understood by those of ordinary skill in the art. Could be.

The encryption method according to the embodiment described below is named BA-RC4. Here, 'BA' means block access, and 'RC4' means stream encryption algorithm applied in the embodiment.

One. Stream  Encryption / Decryption Method

One) Stream  Encryption method

4 is a flowchart illustrating a stream encryption / decryption method according to an embodiment. 5 illustrates a method of constructing a key tree and a method of mapping a subkey and a data block, according to an exemplary embodiment.

Referring to FIG. 4, the stream encryption method according to the embodiment includes a root key generation step S410, a key tree construction step S420, a subkey and a data block mapping step S430, and a ciphertext stream generation step S440. It includes.

Root key generation step ( S410 )

In operation S410, a root key K _{0 , 0} is generated to construct a key tree necessary for encrypting plain text. Here, the root key (K _{0 , 0} ) is a key that only the user knows and corresponds to the key at the top node of the key tree. The one-way hash function preferably uses a securely secure hash function such as Secure Hash Algorithm-1 (SHA-1).

Key tree configuration steps ( S420 )

As shown in FIG. 5, first, a root key K _{0 , 0} is divided into a plurality of subsections. The number (m) of subsections can be set arbitrarily. In an embodiment, the number m is set to four.

Next, the four divided subsections (ABCD) are exchanged through a swapping operation to generate four root keys to be input to the hash function SHA-1. The four root keys have different values and are generated by one exchange operation. For example, assuming that the subsection values of the root key K _{0 , 0} are ABCD, SHA (ABCD), SHA (BACD), SHA (ACBD), SHA You can get the input of a hash function (SHA-1) such as (ABDC).

Next, key values obtained through the swapping operation are inputted to the hash function SHA-1, respectively, and new subkeys K _{1 , 0} , K _{1 , 1} , K _{1 , 2} , K _1,3 ). Accordingly, a key tree having a depth of 1 may be formed by being differentiated from one parent node to a child node.

Next, the sub-keys K _{1 , 0} , K _{1 , 1} , K _{1 , 2} , K _{1 , 3} obtained through the hash function SHA-1 are divided into four subsections. Each subsection value has a different value through a swapping operation, thereby generating four subkeys to be input to the hash function SHA-1. For example, suppose that the subkey obtained through the hash function SHA-1 using SHA (BACD) as an input value is composed of subsection values of A ', B', C ', and D'. Swapping Operation: SHA (A 'B' C 'D'), SHA (B 'A' C 'D'), SHA (A 'C' B 'D'), SHA (A 'B' D 'C'). This value is input to the hash function SHA-1 again to generate new subkeys K _{2 , 0} , K _{2 , 1} , K _{2 , 2} , K _{2 , and 3} . Accordingly, by dividing from one child node to another child node, a key tree having a depth of 2 can be formed.

The key tree can be constructed by extending the key through the above-described methods. In order to obtain a new sub key value for key expansion, values to be input to the hash function SHA-1 should be different from each other. In this embodiment, a method of exchanging subsections is applied. However, the method for obtaining the input value of the hash function SHA-1 is not necessarily limited to the method by the exchange operation, and various methods are applicable.

The key (root key or sub key) according to the embodiment may be represented by the following formula.

In Equation 1, h denotes a depth of a key tree, and s denotes a sequence number of nodes having the same depth h.

는 루트 키를 의미하며, 하나의 부모 키(루트 키 또는 서브 키)

는 4 개의 자식 키

로 분화될 수 있다.

Means the root key, one parent key (root key or subkey)

Four child keys

Can be differentiated into

The key tree according to the embodiment is configured through key expansion, but preferably has a depth h that satisfies the condition expressed by the following equation.

에 의해 5가 된다. 따라서, 깊이(h)가 5인 키 트리를 형성하면 된다.M in Equation 2 represents the number of subsections, n represents the number of data blocks configured in the storage. Therefore, the above-described method may be repeatedly performed until a key tree having a depth h that satisfies Equation 2 is constructed to construct a key tree. For example, suppose a single data block is 4KB in size and there is a total of 2MB of storage, the storage will consist of 512 data blocks (n = 512). At this time, the depth h of the key tree satisfying this is

Becomes 5 by. Therefore, a key tree having a depth h of 5 may be formed.

Assuming that the size of one data block configured in the storage system is 16KB, and a key tree having a depth (h) of 12 is formed by dividing from one parent key to four child keys, the following formula is used. It can cover 256GB of storage.

Subkeys and data blocks Mapping  step( S430 )

In operation S430, as illustrated in FIG. 5, the data blocks B ₀ ..., B _x , B _{x +1} ,..., B _y , B _{y +1} ... B _4h-1 ), respectively. For example, the subkeys “K _{h , x} , K _{h , x + 1} ... K _{h , y} , K _{h , y + 1} ”represent data blocks“ B _x , B _{x + 1} ,... B _y , B _{y +1} ”.

cryptogram Stream  Generation step ( S440 )

6 is a diagram illustrating a process of generating a cipher text stream and storing it in a storage data block according to an embodiment.

In operation S440, plain text (S ₀ ) may be used using respective _subkeys mapped to data blocks B ₀ ..., B _x , B _{x + 1} ,..., B _y , B _{y +1} ... plain text) Encrypt the stream. The data block is encrypted based on the stream encryption algorithm. More specifically, as shown in FIG. 6, an XOR operation of the subkeys 401 and 402 mapped to the corresponding data block and the plaintext streams 501 and 502 to be stored in the corresponding data block are performed by XOR operation, respectively, in an encrypted stream. Produces (601, 602).

As shown in FIG. 6, the first block of the plaintext stream is encrypted using the first subkey (K _{h , 0} ) of depth h generated through the key tree configuration and configured in the storage system 700. It may be stored in the data block B ₀ . In addition, the second block of the plaintext stream may be encrypted using the second sub-key K _{h , 1} of depth h and stored in the second data block B ₁ configured in the storage system 700. The encryption method is based on the stream encryption algorithm. Sub-key K _h corresponds to the first sub-key of the first child node in the left-most of the child nodes in the depths h in the key tree constructed by step S420, the sub-key K _h is the second child node in the next left Corresponds to the subkey. Also in the block structure of the storage system 700, the data blocks B ₀ and B ₁ are the first and second blocks located from the left most.

In the embodiment, it is assumed that there is another key (K _{u , s} ) shared by the Cloud Service Provider and the user in accessing the outsourced storage after performing encryption. After encrypting using a key that only you know (key derived from the key tree), you can use another key (K _{u , s} ) shared by the cloud service provider and the user. Can be. The reason for this double encryption is to ensure confidentiality from other external users when there is an upload or download command from the cloud service provider.

2) Stream  Decryption method

Referring to FIG. 4, the stream decryption method according to the embodiment includes a subkey derivation step S450 and a decryption text stream generation step S460.

Subkey derivation step ( S450 )

In operation S450, subkeys mapped to data blocks of the storage 700 are derived through a hash function. In addition, when decryption is required for a specific block, a subkey of a child node mapped to the block may be derived using a hash function.

Decryption Stream  Generation step ( S460 )

In operation S460, decryption may be performed using the corresponding subkey derived through operation S450. More specifically, the plaintext stream is generated by performing an XOR operation on the derived subkey and the decrypted text stream stored in the corresponding block. In this case, the decryption method is based on a stream encryption algorithm, through which a decrypted text stream may be generated in units of blocks. It is possible not only to decrypt but also to encrypt streams in block units.

Hash operation is very fast because it is about 1/10 more complicated than general encryption algorithm, and it can be derived through very small number of operations in deriving subkey of child node mapped to a specific block. You can derive the key quickly. Accordingly, not only can block accessibility be provided, but also the encryption of each block can be applied to the stream encryption algorithm, thereby providing very fast computational efficiency.

7 is a diagram illustrating an overall process of storing and reading a file using a stream encryption algorithm according to an embodiment.

When the specific information is stored in the storage 700, when a location to store the information is determined, the key mapped to the location to be stored is derived by using the key tree to be encrypted. Subsequently, an additional encryption is performed using a key shared by a storage service provider and a user for communication confidentiality, and then stored in the storage 700.

When specific information is read from the storage 700, the location where the information is stored is found, and the information stored from the outsourced storage is obtained. Thereafter, after decrypting using the key shared by the storage service provider and the user, the key derivation method described above can be used to derive and decrypt the key to read the original stored data.

According to an embodiment, a key tree is constructed through key expansion using a hash function, and each block of the storage is stream-encrypted with a different key derived from the key tree, so that the block encryption algorithm can access the stream encryption algorithm. Can provide computational efficiency.

2. Password file system

8 is a block diagram showing the overall configuration of a cryptographic file system 800 according to an embodiment.

Referring to FIG. 8, an encrypted file system 800 according to an embodiment includes a stream encryption system 810, a stream decryption system 820, and a storage 700. The cipher file system 800 according to the embodiment is an apparatus implemented for the stream encryption / decryption described above, and will be described with reference to FIGS. 3 to 7.

One) Stream  Encryption system (810)

Referring to FIG. 8, the stream encryption system 810 according to the embodiment includes a root key generation unit 811, a key tree construction unit 813, a mapping unit 815, and an encryption operation unit 817.

Root key Generator (811)

The root key generation unit 811 generates a root key K _{0 , 0} in order to construct a key tree necessary for encrypting plain text. Here, the root key K _0,0 is a key that only the user knows and corresponds to the key at the top node of the key tree. The one-way hash function preferably uses a securely secure hash function such as Secure Hash Algorithm (SHA-1).

Key tree Construction (813)

The key tree constructing unit 813 includes an exchange calculating unit (not shown) and a key generating unit (not shown).

The exchange operation unit (not shown) may divide a root key value into a plurality of subsections, and generate a plurality of root keys having different subsection values by dividing each divided subsection. In addition, the value of the subkey may be divided into a plurality of subsections, and each of the divided subsections may be generated through a swap operation to generate a plurality of subkeys having different subsection values.

The key generation unit (not shown) may generate a plurality of root keys generated through the exchange operation unit (not shown) as sub keys having different values using a hash function. In addition, a plurality of subkeys generated through an exchange operator (not shown) may be generated as subkeys having different values using a hash function.

Hereinafter, a method of constructing a key tree through an exchange operator (not shown) and a key generator (not shown) will be described in more detail.

First, the exchange operation unit (not shown) may divide a root key value K _{0 , 0} into a plurality of subsections. Here, the number of subsections may be arbitrarily set, and in the embodiment, the number of subsections is set to four.

Next, the exchange operation unit (not shown) may generate four root keys to be input to the hash function SHA-1 by exchanging the four subsections ABCD through a swapping operation. . The four root keys have different values and are generated through one exchange operation. For example, assuming that the subsection values of the root key K _{0 , 0} are ABCD, SHA (ABCD), SHA (BACD), SHA (ACBD), SHA You can get the input of a hash function (SHA-1) such as (ABDC).

The key generator (not shown) inputs the key values obtained through the exchange operator (not shown) to the hash function SHA-1, respectively, and sets new subkeys K _{1 , 0} , K _{1 ,} which have different values _{. 1} , K _{1 , 2} , K _1,3 ). Accordingly, a key tree having a depth of 1 may be formed by being differentiated from one parent node to a child node.

Next, the key generation unit (not shown) again resets the values of the sub-keys K _{1 , 0} , K _{1 , 1} , K _{1 , 2} , K _{1 , 3} obtained through the hash function SHA-1. It can be divided into subsections. In addition, each subsection value has a different value through a swapping operation, thereby generating four subkeys to be input to the hash function SHA-1. For example, suppose that the subkey obtained through the hash function SHA-1 using SHA (BACD) as an input value is composed of subsection values of A ', B', C ', and D'. Swapping Operation: SHA (A 'B' C 'D'), SHA (B 'A' C 'D'), SHA (A 'C' B 'D'), SHA (A 'B' D 'C'). This value is input to the hash function SHA-1 again to generate new subkeys K _{2 , 0} , K _{2 , 1} , K _{2 , 2} , K _{2 , and 3} . Accordingly, by dividing from one child node to another child node, a key tree having a depth of 2 can be formed.

The key tree constructing unit 813 may construct a key tree while extending the key through the above-described methods. In order to obtain a new sub key value for key expansion, values to be input to the hash function SHA-1 should be different from each other. In this embodiment, a method of exchanging subsections is applied. However, the method for obtaining the input value of the hash function SHA-1 is not necessarily limited to the method by the exchange operation, and various methods are applicable.

The key (root key or sub key) according to the embodiment may be represented by the following formula.

In Equation 4, h denotes a depth of a key tree, and s denotes a sequence number of nodes having the same depth h.

는 루트 키를 의미하며, 하나의 부모 키(루트 키 또는 서브 키)

는 4 개의 자식 키

로 분화될 수 있다.

Means the root key, one parent key (root key or subkey)

Four child keys

Can be differentiated into

The key tree according to the embodiment is configured through key expansion, but preferably has a depth h that satisfies the condition expressed by the following equation.

에 의해 5가 된다. 따라서, 깊이(h)가 5인 키 트리를 형성하면 된다.M in Equation 5 denotes the number of subsections, and n denotes the number of data blocks configured in the storage 700. Accordingly, the above-described method may be repeatedly performed until a key tree having a depth h that satisfies Equation 5 is constructed, thereby constructing a key tree. For example, suppose a single data block is 4KB in size and there is a total of 2MB of storage, the storage will consist of 512 data blocks (n = 512). At this time, the depth h of the key tree satisfying this is

Becomes 5 by. Therefore, a key tree having a depth h of 5 may be formed.

Assuming that the size of one data block configured in the storage system is 16KB, and a key tree having a depth (h) of 12 is formed by dividing from one parent key to four child keys, the following formula is used. It can cover 256GB of storage.

Mapping section (815)

As illustrated in FIG. 5, the mapping unit 815 may include the data blocks B ₀ ... B _x , B _{x + 1} ,... B configured in the storage 700 and the sub keys generated through the key tree configuration unit 813. _y , B _{y + 1} ... B _4h-1 ), respectively. For example, the subkeys “K _{h, x} , K _{h, x + 1} ... K _{h, y} , K _{h, y + 1} ”represent data blocks“ B _x , B _{x +1} ,... B _y , B _{y +1} ”.

encryption Calculator (817)

The encryption operation unit 817 uses the plain text ( _subtexts ) mapped to the data blocks B ₀ ... B _x , B _{x + 1} , ... B _y , B _{y + 1} ... B _{4h-1 of the storage} . plain text) The stream can be encrypted. The data block is encrypted based on the stream encryption algorithm. More specifically, as shown in FIG. 6, an XOR operation of the subkeys 401 and 402 mapped to the corresponding data block and the plaintext streams 501 and 502 to be stored in the corresponding data block are performed by XOR operation, respectively, in an encrypted stream. (601, 602) can be generated.

2) Stream  Decryption System (820)

The stream decryption system 810 according to the embodiment includes a key derivation unit 821 and a decryption operation unit 823.

Key guidance unit 821

The key derivation unit 821 derives the subkeys mapped to the data block of the storage 700 through a hash function. In addition, when decryption is required for a specific block, a subkey of a child node mapped to the block may be derived using a hash function.

Decrypt Calculator (823)

The decryption operation unit 823 may perform decryption using the corresponding subkey derived through the key derivation unit 821. More specifically, the plaintext stream is generated by performing an XOR operation on the derived subkey and the decrypted text stream stored in the corresponding block. At this time, decryption is performed based on the stream encryption algorithm, and through this, a decryption text stream may be generated in units of blocks. It is possible not only to decrypt but also to encrypt streams in block units.

9 is a graph illustrating a performance comparison of the stream encryption algorithm BA-RC4, the conventional block encryption algorithm AES, and the stream encryption algorithm RC4 according to the embodiment.

In the graph of FIG. 9, the horizontal axis represents a starting address for accessing storage, and the vertical axis represents throughput. The higher the throughput, the better. The graph obtained in this experiment is a measure of throughput by changing the starting address to access a 1MB file and assuming that a block of storage is 16KB.

In the case of the block encryption algorithm (AES), since encryption / decryption is performed on a block basis, a certain throughput is shown regardless of the access position.

On the other hand, in the case of the stream encryption algorithm RC4, the throughput gradually decreases as the starting address position (number) to be accessed increases. In order to read a particular block, the stream encryption algorithm (RC4) must generate a random sequence that was used to encrypt that block, and in order to do so, it must generate a random sequence using the initial key value until the corresponding state is obtained. As a result, random accessibility is very low. Accordingly, it can be seen that as the approaching position increases, the time taken to derive the key gradually increases, so that the overall throughput also decreases.

As described above, those skilled in the art to which the present invention pertains will understand that the present invention may be implemented in other specific forms without changing the technical spirit or essential features.

Therefore, the embodiments described above are to be understood in all respects as illustrative and not restrictive, and the scope of the present invention is indicated by the following claims rather than the above description, and the meaning and scope of the claims And all changes or modifications derived from the equivalent concept should be interpreted as being included in the scope of the present invention.

Claims (11)

As a stream encryption method in a cipher file system,
Generating a root key for use in file system encryption;
Constructing a key tree by generating a plurality of subkeys from the root key through a hash function;
Mapping a plurality of sub keys configured in the key tree and data blocks configured in storage of the cryptographic file system; And
Generating a ciphertext stream by performing an XOR operation on the plurality of subkeys mapped to the data blocks and the plaintext stream.
Hash tree-based stream encryption method comprising a.
The method of claim 1,
Comprising the key tree,
a. Dividing a value of the root key into a plurality of subsections and generating a plurality of root keys having different subsection values through position exchange between the divided subsections;
b. Generating a plurality of root keys generated through the step a as sub keys having different values using a hash function;
c. Dividing the value of the subkey generated through the step b into a plurality of subsections, and generating a plurality of subkeys having different subsection values through position exchange between the divided subsections; And
d. Generating a plurality of subkeys generated through the step c as subkeys having different values using a hash function,
Comprising a key tree while expanding the sub-key through the steps a to d, and comprises a key tree to the depth (h) of the key tree that satisfies the following formula,

m is the number of the subsections,
n is the number of data blocks, hash tree-based stream encryption method.
A method of decrypting the ciphertext stream generated according to the method of claim 1,
Deriving a plurality of subkeys mapped to data blocks of the storage through a hash function; And
Generating a decrypted text stream by performing an XOR operation on the ciphertext stream and the plurality of sub keys derived through a hash function
Hash tree-based stream decoding method comprising a.
The method of claim 3,
The ciphertext stream stored in the storage can be accessed in units of data blocks.
A system for stream encryption,
A root key generation unit generating a root key for use in encrypting the file system;
A key tree construction unit generating a plurality of sub keys from the root key through a hash function to construct a key tree;
Storage including a plurality of data blocks for storing a ciphertext stream;
A mapping unit for mapping the plurality of sub keys configured in the key tree and data blocks of the storage; And
An encryption operation unit generating an encrypted text stream by performing an XOR operation on the plurality of sub keys mapped to the data blocks of the storage and the plain text stream.
Password file system comprising a.
The method of claim 5,
The key tree configuration unit,
An exchange operation unit and a key generation unit,
The exchange operation unit,
Dividing the value of the root key into a plurality of subsections, and generating a plurality of root keys having different subsection values through position exchange between the divided subsections,
Dividing a value of the sub key into a plurality of subsections, and generating a plurality of subkeys having different subsection values through position exchange between the divided subsections,
The key generation unit,
Generating a plurality of root keys generated through the exchange operation unit as sub keys having different values using a hash function,
Generating a plurality of subkeys generated through the exchange operation unit as subkeys having different values using a hash function,
The key tree configuration unit,
Comprising a key tree while extending the sub-key through the exchange operation unit and the key generation unit, and constitutes a key tree with a depth (h) of the key tree that satisfies the following formula,

m is the number of the subsections,
n is the number of data blocks.
A system for decrypting the ciphertext stream generated according to the cipher file system of claim 5,
A key derivation unit for deriving a plurality of sub keys mapped to the data block of the storage using a hash function; And
A decryption calculator configured to generate a decrypted-text stream by performing an XOR operation on the plurality of sub-keys derived from the key derivation unit and the ciphertext stream.
Password file system comprising a.
The method of claim 7, wherein
The ciphertext stream stored in the storage is accessible in data block units.
A system for stream encryption and decryption,
A root key generation unit generating a root key for use in encrypting the file system;
A key tree construction unit generating a plurality of sub keys from the root key through a hash function to construct a key tree;
Storage including a plurality of data blocks for storing a ciphertext stream;
A mapping unit for mapping the plurality of sub keys configured in the key tree and data blocks of the storage; And
An encryption operator configured to generate a ciphertext stream by performing an XOR operation on the plurality of subkeys mapped to the data blocks of the storage and the plaintext stream;
A key derivation unit for deriving a plurality of sub keys mapped to the data block of the storage using a hash function; And
A decryption calculator configured to generate a decrypted-text stream by performing an XOR operation on the plurality of sub-keys derived from the key derivation unit and the ciphertext stream.
Password file system comprising a.
10. The method of claim 9,
The key tree configuration unit,
An exchange operation unit and a key generation unit,
The exchange operation unit,
Dividing the value of the root key into a plurality of subsections, and generating a plurality of root keys having different subsection values through position exchange between the divided subsections,
Dividing a value of the sub key into a plurality of subsections, and generating a plurality of subkeys having different subsection values through position exchange between the divided subsections,
The key generation unit,
Generating a plurality of root keys generated through the exchange operation unit as sub keys having different values using a hash function,
Generating a plurality of subkeys generated through the exchange operation unit as subkeys having different values using a hash function,
The key tree configuration unit,
Comprising a key tree while extending the sub-key through the exchange operation unit and the key generation unit, and constitutes a key tree with a depth (h) of the key tree that satisfies the following formula,

m is the number of the subsections,
n is the number of data blocks.
10. The method of claim 9,
The ciphertext stream stored in the storage is accessible in block units.

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